Valvoline 4-stroke Motorcycle Oil

"Without telling us, they put a synthetic blend in her car and in a couple of days, it was smoking, burning a quart of oil every 500 miles and leaking oil from seals."

don't get upset, but your credibility just took a hit with that,, maybe you should have added a dose of your MotorKote.

Motor oil is motor oil, synthetic can have better properties than motor oil made from crude. Assuming that the SAE weight of the oil is comparable, synthetic will not leak more or burn more than conventional motor oil.